What do you think the new challenge tower reward will be

The "Klassic" DLC alts from the console game that came in the compatibility packs or were pre-order exclusives are already unlocked on the Vita from the start. No need to unlock those, so that rules out them as the final prize which I agree would be silly.

My only guess is boss characters playable or some other odd thing like the rumored new characters. Time will tell I guess.